In my lay opinion, being neither a lawyer nor the operator of a web site, this would appear to be "good to go".
I did have to look up the Lex Julia Majestatis. When I did so, Google included references to the Lex Iulia Maiestatis, which is a 48 BC law attributed to Julius Caesar regarding treason. I'm not sure where we come down on the interchange between J and I in cases like this, but I note the fact. That is probably an excellent question for the RFC Editor.
As to the operational details, it presumes some sort of database entry maintained by operator of the indicated web site or accessible as a service by the site that can determine, for a stated URI, whether there is a legal issue with the URI. The URI may or may not represent content actually accessible by via web site; the document clearly states that when the legal block is removed, the content may still be inaccessible. The detail of the type of block are left to the referenced site to describe in prose, and so depend on no special coding in browsers etc beyond the implementation of the code.
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